Glucose transporter protein-independent tumor cell accumulation of fluorine-18-AFDG, a lipophilic fluorine-18-FDG analog.
Fluorine-18-fluorodeoxyglucose (FDG) is used clinically for tumor diagnosis, but its mechanism of accumulation in tumor cells is complicated because two factors, glucose transporter protein (GLUT) and hexokinase, govern [18F]FDG uptake directly. We selected a lipophilic [18F]FDG analog, 1,3,4,6-tetra-acetyl-2-[18F]-2-deoxy-D-glucose ([18F]AFDG), to regulate the effects of hexokinase and evaluated its characteristics in an in vitro cell culture system.


METHODS
Fluorine-18-AFDG was synthesized by the method used to produce [18F]FDG, as an intermediate of [18F]FDG. Fluorine-18-AFDG uptake study was performed with LS180 tumor cells, and its metabolites were also investigated by thin-layer chromatography. To evaluate the relationship between [18F]AFDG and GLUT, we also examined [18F]AFDG uptake in the presence of cytochalasin B or with increased medium glucose concentration. The effects of lowered temperature (4 degrees C) on [18F]AFDG uptake were also investigated.


RESULTS
Fluorine-18-AFDG (lipophilicity: octanol/water = 3.5) uptake was 3.3-fold higher than that of [18F]FDG. Metabolic analysis showed that [18F]AFDG was extremely stable in the incubation medium but was quickly hydrolyzed and metabolized to 2-fluoro-[18F]-2-deoxy-D-glucose-6-phosphate ([18F]FDG-6P) in tumor cells. Fluorine-18-FDG-6P accounted for approximately 45% of the total radioactivity after a 60-min incubation of [18F]AFDG. Incubation with 50 microM cytochalasin B did not affect [18F]AFDG uptake. In medium with double the control glucose level, [18F]FDG uptake was decreased by about 50%, but [18F]AFDG uptake was not affected. Fluorine-18-AFDG uptake and [18F]FDG-6P production did not show saturation and increased linearly with addition of a 10-fold higher concentration of [18F]AFDG. Lowered incubation temperature caused decreased [18F]AFDG uptake due to reduced [18F]FDG-6P production.


CONCLUSIONS
Fluorine-18-AFDG rapidly penetrated the cell membrane as a result of its high lipophilicity and was metabolized to [18F]FDG-6P within cells. Fluorine-18-AFDG was thus characterized as "GLUT-independent [18F]FDG."
Waki
A
A
Biomedical Imaging Research Center, Fukui Medical School, Japan.
Fujibayashi
Y
Y
Magata
Y
Y
Yokoyama
A
A
Sadato
N
N
Tsuchida
T
T
Ishii
Y
Y
Yonekura
Y
Y
D003571:Cytochalasin B / Q000494:pharmacology; D003847:Deoxyglucose / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D019788:Fluorodeoxyglucose F18 / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D005947:Glucose / Q000378:metabolism; D006801:Humans; D009004:Monosaccharide Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000378:metabolism
C110723:1,3,4,6-tetraacetyl-2-fluoro-2-deoxyglucose; D009004:Monosaccharide Transport Proteins; D019788:Fluorodeoxyglucose F18; D003571:Cytochalasin B; D003847:Deoxyglucose; D005947:Glucose